Method of making acetic anhydride from lignified cellulose



April 17, 1962 A. M. THoMsEN 3,030,277

METHOD oF MAKING AcETIc ANHYDRIDE FROM LIGNIFIED CELLULosE Filed April e. 195s 7i tar Lmmm5 l l am INVENTOR.

' 3,030,277 METHD F MAKING ACE'I'IC ANHYDRIDE lllRll/l LIGNIJFED CELLULOSE Atti-ed lV. Thomsen, 265 Buciinglirannl Way, Apt. 402,

t San Francisco, Calif. Filed Apr. 6, i959, Ser. No. 804,488 Claims. (Cl. 13S-39) As the title indicates, the object of my process is to obtain the maximum amount of acetic anhydride as the principal product. As important by-products, some vanillin is also obtained, and to ya minor extent, yeast. I lwill rst describe my process briefly and then take a preferred version, which I have set down in the drawing, in which I will specifically point out my invention and so describe each and every step that it can be followed without difculty by any competent operator.

The iirst step in my process is to separate the cellulose 'from' the lignin and other incrustants by a well known type of cooking, namely, the neutral sulphite cook. I have selected this as the approach wherein there is least destruction of cellulose, hence the largest yield of pulp, though same is also somewhat impure. Said pulp is then treated by itself and likewise the spent cooking liquor. Both, in diverse ways, yield acetic acid which appears as sodium acetate. Simultaneously some vanillin is set -ree in such a 'form that it is easily recovered. Finally,

when I convert my pulp into sugar and then ferment same for alcohol, I ind that `a portion of my sugar, derived from pentoses is unfermentable. However, at. a later stage with much aeration this forms excellent yeast food so I utilize the last of my sugar in this manner.

I will now proceed to describe my drawing as the simplest way of elucidating my process. In the upper left hand corner, I commence by showing a saturator which is merely an agitated tank in which wood, or, in the larger sense, any type of ligniiied cellulose, is fully saturated with hot cooking liquor. In the lower left hand corner I have shown the composition of a regenerated cooking liquor as a solution of neutral sodium sulphite. After such saturation said wood is treated in the digester, at the upper right, with steam at approximately 175 lbs. gage pressure for several hours, or until the -wood is substantially de-ligniiied, when said digester is discharged into the blowpit in the conventional manner.

Separation is here made between the pulp `and the spent cooking liquor land the pulp most thoroughly washed. Pulp iand spent cooking liquor issuing from the blowpit are now subjected to diverse treatments as sho-wn by the left hand and the right hand columns of the drawing, respectively. I will first rfollow the course taken by the pulp. It is passed on to a sacchariliei which is but `another digester operating on a continuous basis, a constant discharge through a nozzle being made possible by steadily pumping in the pulp suspension. I have also shown that sulphuric 'acid is added. The amount will Vary as the physical Icharacter of the pulp may determine, but in general it may be taken as about l0 pounds per ton o-f solution in which the pulp is suspended. Obviously, said digester and all its fittings must be suited to said acid digestion.

By this treatment the pulp is substantially converted into sugar, the cellulose proper giving a fermentable hexose sugar, the pentose a similar pentose sugar which is regarded as uonfermentable, that is, it is refused by the type of yeast conventionally employed in alcoholic fermentation. Owing to the gentle character of the initial cooking step, the pulp not only retains much pentose material but also some lignin. This latter is left as a residue on saccharilication and is passed over to the spent liquor division for further treatment.

3,030,277 Patented Apr. 17,1952

, The sugar solution then passes into the 'fermenters, a series of closed tanks, in order that the carbon dioxide produced in fermentation may be collected and used in the carbonaton also a portion of the spent liquor division. In the fermenters I have shown the liquor progressively passing from fermenter to fermenter, while a portion of the contents of the last fermenter is continuously re-cycled to the first fermenter. I have also shown the lacidity of the sugar solution corrected to the pH most favored by the yeast by the addition of the requisite caustic soda int-o the trst fermenter.

Fermentation is judged complete when only a modicum of hexose sugar remains in the third fermenter. The yeast is then separated and the solution passed on to an evaporator where approximately one-half of the liquor is evaporated. The condensate from said evaporator is thus enriched in alcohol -by approximately and the concentrate is e uall enriched in entose sugarsl Cl P e and yeast nutrients. The need of these, as -well as the need to retain the fermenters at the most yfavorable temperature is too obvious to require comment.

This concentrate is next cooled, commingled with the yeast previously separated, and strongly aeriated in order to induce a vigorous growth of yeast until substantially all contained sugar has been consumed. As a commercial product, feed yeast, this yeast is next separated and the de-sugared solution is re-cycled, in part, to the blowpit formerly described. Here it serves as wash water for the pulp and for the liquid medium in which the pulp is suspended as it is pumped to the sacchariiier. Another portion of the de-sugared liquid is used at a subsequent stage as the liquid in which certain ashes from a furnace are dissolved and thus fully re-cycled so that all dissolved matters remaining thereinmay, ultimately, be utilized. Y

The condensate from the evaporator, enriched in alcohol, is next sent to the oxidizer, the conventional device used in the so-called quick vinegar process. In the presence of ample air, and the lilms of the organism, Bacterum aceti, which coat the packing of the oxidizer, said alcohol is converted into dilute acetic acid, the yield bei-ng approximately on the weight of the alcohol involved. Inasmuch asthis step is entirely conventional no further description seems needed.

In the drawing I have shown this dilute acid as passing to the spent liquor division for the conversion of said acetic acid into sodium acetate, the devices indicated being the primary and secondary leachers, respectively. In the iirst of these steps both caustic soda and sodium carbonate are present, in the second -step much carbonate remains unused, hence is now used to neutralize this weak form of acetic acid at the same time that itV furnishes the water solution needed to dissolve all preformed sodium acetate.

Attention will no-W `be given to the spent cooking liquor leaving the blowpit. I have shown this liquor as commingled with caustic soda in the digester following after the blowpit. The amount is roughly the same, by weight, as the total organic material present in the liquor, and the temperature is that corresponding to a gage pressure of pounds and the time approximately 3 hours or less. Fromv this -digester the liquid passes to the carbonator where it meets the carbon dioxide from the fermenters in any conventional absorption device. After such digestion and carbonation a certain amount of vanillin has been formed and prepared for extraction with a specific solvent. I nd that any one of the higher alcohols is acceptable, but I prefer the use of butyl alcohol. I thus obtain a solution of vanillin in the selected solvent and an extracted residual. Said residual is next seen advanced to the fusionkettle, an agitated evaporating device of any type where said residue is commingled with additionalv caustic soda Qj in such an amount that the soda shall constitute approximately 75% of the total solids in 4the mixture. By evaporation, the fusion temperature is allowed to reach approximately 230 C., when the formation of sodium acetate will be at its maximum.

The fusion mixture is then sent to the primary leacher where just enough of the dilute acetic acid, previously described, is added so that virtually all the caustic soda remaining after the fusion-reaction is finished is dissolved away, and in part converted to sodium acetate. At the same time most of the sodium acetate produced during the fusion step will likewise go into solution. Separation is then made between liquid and solids, the latter being decomposed organics, sodium carbonate, and sodium oxalate which has a veryk low solubility. The solution is crystallized for sodium acetate and a mother liquor consisting essentially of caustic soda which is re-cycled, in part to the fusion step and in part to the vanillin-digestion step.

The residue from this primary leaching step is next passed on to the secondary leacher where additional dilute acetic acid is used to remove more sodium carbonate in the form of acetate as well as much of the carbonate as such. Separation is once more made between solids and liquids, the former being sent to the furnace while the latter is used to dissolve the ashes from the furnace. Said ashes are essentially sodium carbonate with some sodium sulphate, the furnacing being performed in such a manner as to avoid fusion with attendant formation of sulphides.

For this reason the furnacev selected must be of the oxidizing type, such as the rotary kiln, acting as a roaster, or a Herreshol with its constantly rabbled charge. The ash is discharged into the dissolver, merely an agitated tank, in which it meets the solution from the secondary leacher, and also the spent fermentation liquor from the yeast grower, not previously re-cycled to the blowpit.

The solution thus formed in the dissolver is next divided into two parts,V one part being caustic-ized in the conventional calcium hydroxide reaction in order to meet the caustic soda requirements of my process. The remainder is passed on to the decomposer where i-t is commingled with the calcium carbonate from the causticizing step and with sulphur dioxide. The resulting slurry is iiltered giving as a reject the calcium sulphate shown on the drawing, and a solution of the neutral or normal sulphite of Sodium, thus regenerating the cooking liquor originally employed in the saturator.

Two supplementary steps also appear on the drawing. It is obvious that in the vanillin-extraction step considerable of the solvent will remain in the extracted residue and would necessitate an additional step for its recovery. However, if the next step be the fusion step, then it is unavoidable that all such solvent must be volatilized. Furthermore, the methoxyl -group in the wood will, in part, appear as methanol, so Iboth substances will -be recovered simultaneously from the fusion step. Likewise, I have shown the conversion of the sodium acetate, previously recovered, into acetic anhydride, in the lower right corner of the drawing. While not mandatory it is economically necessary, the anhydride weighing less and costing more than the acid or its soda salt. Considering the respective locations of our forest areas, where the operation would take place, and the consuming market far away, the advantage of this step will be obvious.

Having thus described in full detail my process in its preferred and fully integrated form I wish tor call attention to sundry abbreviations or substitutions. Thus it is evident that spent fermentation liquor could be substituted for the dilute acetic acid in the leaching steps, or plain water. Likewise, said dilute acid could be sent to the dissolver and there neutralized with the furnace ashes, without seriously changing any economic aspect. It is also plain that sundry portions of my disclosure could be lifted out of the composite and used elsewhere.

Thus, pulp from any source could be 1used as raw material for making the dilute acetic acid shown on the drawing, with yeast as the supplementary means for utilizing the non-fermentable sugars unavoidably produced from the pentoses in the sacchariication step. Similarly, any spent cooking liquor from a sulphite cook on coniferous woods could be used as raw material for the vanillin digestion followed by a caustic fusion, said vanillin and sodium acetate being the sole products. Whether any such divergence would prove profitable is beside ythe matter. Obviously, I consider such abbreviations as within the limits of my disclosure.

Having thus fully described my process, I claim:

1. The method of making acetic anhydride from lignitied cellulose which comprises; digesting said lignitied cellulose with a solution of sodium sulphite under the conventional conditions as to sodium sulphite concentration, time and temperature until the fibers of said ligniied cellulose shall have been substantially freed from incrusting substances; separating said ibers from the spent cookingl that there shall be present approximately 3 pants of soda for one part of organics and fusing at a finishing temperature of approximately 230 C.; recovering the retained solvent present in said residue and the methanol produced in the fusion simultaneously; leaching the fused mass with a watery liquid in a two-step leaching; separating sodium acetate by crystallization from the lirst leach liquor and re-cycling the mother liquor to the vanillin digestion step and the fusion step respectively; reserving the second leach liquor for a subsequent step; furnacing the residual from the leaching step in an oxidizing roast to produce a mixture of sodium carbonate and sulphate; dissolving the ash from said furnacing in the reserved portion of leach liquor and dividing into two parts; causticiding one with lime to yield the caustic soda called for, and commingling the remainder with calcium carbonate and with sulphur dioxide to produce calcium sulphate and sodium'sulphite; separating the former and re-cycling the latter as the original digesting medium; commingling the reserved pulp with approximately a 1/2% solution of sulphuric acid, heating for a matter of minutes at approximately l5() pounds gage pressure to partially saccharify same; separating sugar solution from residual liber, and recycling said ber to the sacchan'fying operation; fermenting the resulting sugar solution for alcohol; removing said alcohol by evaporation and condensation; oxidizing the condensate to acetic acid and commingling same with the sodium acetate solution previously obtained thus unifying the two types of acetic acid; distilling the sodium acetate collectively obtained with P205 to obtain acetic anhydride-and sodium phosphate.

2. The method of making acetic anhydride from ligniiied cellulose which comprises; digesting said ligniiied cellulose with a solution of substantially neutral sodium sulphite under conventional conditions as to time, temperature, and concentration of sulphite until the fibers of said lignied cellulose shall have been substantially freed from incrusting substances; separating said fibers from said spent cooking liquor; suspending said fibers as a pulp in a dilute solution or" sulphuric acid containing approximately 1/2 of said acid and heating said mixture for a matter of'minutes at approximately 15'0 pounds gage pressure; separating the resultant sugar solution from residual iber and re-cycling said iber once more to the saccharifying operation; separating any unsacchariied residual matter and re-cycling same to the spent cooking liquor; fermenting the sugar solution thus obtained with an appropriate yeast in the conventional manner, lirst neutralizing excess acidity over that advantageous to the yeast by the addition of soda prior to the yeast addition; passing said fermenting liquor through a series of vessels until substantially all fermentable sugar shall have been decomposed into carbon dioxide and ethyl alcohol; collecting the carbon dioxide thus produced and reserving it for the further Itreatment of the spent cooking liquor; separating the yeast from the fully fermented liquor and reserving it for further treatment; evaporating the weak alcoholic liquor until approximately one-half shall have been evaporated and condensing the vapors; cooling the residual liquor in the evaporator and commingling it once more in an aerated, agitated, vessel with the yeast previously reserved until all non-fermentable sugars namely, the pentose sugars unavoidably produced in the sacchariiication step which pa-ss unchanged through the fermentation step but become excellent food for yeast growth, per se, when highly aerated, shall have been utilized as yeast food and separating said yeast; oxidizing the condensate from the evaporating step in the conventional quick vinegar manner, in the presence of air and the appropriate bacterial culture until substantially all the resident alcohol shall have been converted to acetic acid; neutralizing the resultant acid liquor with a basic sodium compound so as to convert said acetic acid into sodium acetate; evaporating and crystallizing out said sodium acetate; commingling said separated acetate with suicient phosphorus pentoxide to combine with said acetate thus yielding acetic anhydride and sodium phosphate, and distilling olf the anhydride from the residual phosphate of sodium.

3. The method of making acetic anhydride set forth in claim 2, with the added step tha-t a portion of the fermenting liquor in the alcohol fermentation procedure be continuously returned from the last fermentation vessel to the first in the series.

4. The method of making acetic anhydride set forth in claim 2, with the added step that the liquor remaining after yeast removal from. the final, aerated yeast growing step be recycled as the liquid medium for the pulp suspension, acidification, and sacchariication prescribed therein.

5. The method of making acetic anhydride from lignified cellulose which comprises; digesting said ligniied cellulose with a solution of sodium sulphite under the conventional conditions as to sodium sulphite concentration, time and temperature until the bers of said liguified cellulose shall have been substantially freed from incrusting substances; separating said fibers from the spent cooking liquor-and reserving said fibers for future treatment; commingling said cooking liquor with suicient caustic soda so that the caustic shall be approximately equal in amount to `the organics present in said liquor and digesting the mixture for approximately 3 hours at 150 C., approximately, until the maximum conversion to vanillin has taken place; carbonating the cooled, digested liquor with carbon dioxide; extracting the liberated vanillin with a suitable solvent; commingling Athe extracted residue with sufficient additional caustic soda so that there shall be present approximately 3 parts of caustic soda for each part of organics; fusing at a linishing temperature of approximately 230 C.; recovering the solvent retained in the residue and the methanol formed in the fusion step by condensation of the vapors emanating from the fusion step; leaching the fused mass with a watery liquid in sufficient amount that substantially all unused caustic soda and the sodium acetate produced shall be present in solution and separating said solution from the residue; evaporating and crystallizing Asaid solution to obtain crystals of sodium acetate and a mother liquor consisting essentially of caustic soda; re-cycling said mother liquor, in part, to the vanillin digestion step and the remainder to the fusion step as a part of the caustic soda requirements; furnacing the residue from the leaching step in an oxidizing roast to remove all organic compounds leaving as an ash essentially the carbonates and sulphates of sodium; dissolving said ash in water and dividing the solution thus formed into two parts; causticizing the one part with lime in the conventional manner thus obtaining a solution of caustic soda for the requirements of the vanillin digestion and fusion steps, respectively, over and above that already supplied by re-cycled mother liquor; commingling the calcium carbonate obtained in said causticizing step with the remainder of the ash-solution previously described, and with sulphur dioxide to produce a solution of sodium sulphite and an insoluble residue of calcium sulphate; removing said calcium sulphate and re-cycling the resultngsolution of neutral sodium sulphite to the first digestion step for fiber liberation as the cooking liquor specified therein; finally, commingling the sodium acetate previously made with suiiicient phosphorus pentoxide to combine with such acetate to yield acetic anhydride and sodium phosphate and distilling o said anhydride from the residue of sodium phosphate.

References Cited in the tile of this patent UNITED STATES PATENTS 806,932 Sommer Dec. l2, 1905 1,912,747 White et al June 6, 1933 2,510,668 Thomsen June 6, 1950 2,752,394 Sorenson et al June 26, 1956 OTHER REFERENCES Underkotier et al.: Industrial Fermentations, 1954, Chemical Publishing Co., N.Y., vol. 1, pp. -171.

Fieser and Fieser. Organic Chemistry, 2nd Edition, page 696. 

1. THE METHOD OF MAKING ACETIC ANHYDRIDE FROM LIGNIFIED CELLULOSE WHICH COMPRISES; DIGESTION SAID LIGNIFIED CELLULOSE WITH A SOLUTION OF SODIUM SULPHITE UNDER THE CONVENTIONAL CONDITIONS AS TO SODIUM SULPHITE CONCENTRATION, TIME AND TEMPERATURE UNTIL THE FIBERS OF SAID LIGNIFIED CELLULOSE SHALL HAVE BEEN SUBSTANTIALLY FREED FROM INCRUSTING SUBSTANCES; SEPARATING SAID FIBERS FROM THE SPENT COOKING LIQUOR AND RESERVING SAID FIBERS FROM FUTURE TREATMENT; COMMINGLING SAID COOKING LIQUOR WITH SUFFICIENT CAUSTIC SODA SO THAT THE CAUSTIC SHALL BE APPROXIMATELY EQUAL IN AMOUNT TO THE ORGANICS PRESENT IN SAID LIQUOR AND DIGESTING SAME FOR APPROXIMATELY 3 HOURS AT 150*C, UNTIL THE MAXIMUM CONVERSION TO VANILLIN HAS TAKEN PLACE; CARBONATING THE COOLED, DIGESTED LIQUOSR WITH CARBON DIOXIDE; EXTRACTING THE LIBERATED VANILLIN WITH A SUITABLE SOLVENT; COMMINGLING THE EXTRACTED RESIDUE WITH SUFFICIENT ADDITIONAL CAUSTIC SODA SO THAT THERE SHALL BE PRESENT APPROXIMATELY 3 PARTS OF SODA FOR ONE PART OF ORGANICS AND FUSING AT A FININSHING TEMPERATURE OF APPROXIMATELY 230*C, RECOVERING THE RETAINED SOLVENT PRESENT IN SAID RESIDUE AND THE METHANOL PRODUCED IN THE FUSION SIMULTANEOUSLY; LEACHING THE FUSED MASS WITH A WATERY LIQUID IN A TWO-STEP LEACHING; SEPARATING ING SODIUM ACETATE BY CRYSTALLIZATION FROM THE FIRST LEACH LIQUOR AND RE-CYCLING THE MOTHER LIQUOR TO THE VANILLIN DIGESTION STEP AND THE FUSION STEP RESPECTIVELY; RESERVING THE SECOND LEACH LIQUOR FOR A SUBSEQUENT STEP; FURNACING THE RESIDUAL FROM THE LEACHING STEP IN AN OXIDIZING ROAST TO PRODUCE A MIXTURE OF SODIUM CARBONATE AND SULPHATE; DISSOLVING THE ASH FROM SAID FURNACING IN THE RESERVED PORTION OF LEACH LIQUOR AND DIVIDING INTO TWO PARTS; CAUSTICIDING ONE WITH LIME TO YEILD THE CAUSTIC SODA CALLED FOR, AND COMMINGLING THE REMAINDER WITH CALCIUM CARBONATE AND WITH SULPHUR DIOXIDE TO PRODUCE CALCIUM SULPHATE AND SODIUM SULPHITE; SEPARATING THE FORMER AND RE-CYCLING THE LATTER AS THE ORIGINAL DIGESTING MEDIUM; COMMINGLING THE RESERVED PULP WITH APPROXIMATELY A 1/2% SOLUTION OF SULPHURIC ACID, HEATING FOR A MATTER OF MINUTES AR APPROXIMATELY 150 POUNDS'' GAGE PRESSURE TO PARTIALLY SACCHARIFY SAME; SEPARATING SUGAR SOLUTION FROM RESIDUAL FIBER, AND RECYCLING SAID FIBER TO THE SACCHARIFYING OPERATION; FERMENTING THE RESULTING SUGAR SOLUTION FOR ALCOHOL; REMOVING SAID ALCOHOL BY EVAPORATION AND CONDENSATION; OXIDIZING THE CONDENSATE TO ACETIC ACID AND COMMINGLING SAME WITH THE SODIUM ACETATE SOLUTION PREVIOUSLY OBTAINED THUS UNIFYING THE TWO TYPES OF ACETIC ACID; DISTILLING THE SODIUM ACETATE COLLECTIVELY OBTAINED WITH P2O5 TO OBTAIN ACETIC ANHYDRDRIDE AND SODIUM PHOSPHATE. 